Yes they tried to patent their sound but if I remember correctly they couldn't. The inturn patented the head angles etc on them. Those patents ran out quite some time back though which is they companies like zippers, merch, s&s and so forth started building motors. You can even buy panhead and knuckleheads that are modern now. It's a pretty sweet deal.
Hubby knows all that stuff.
I ought to run in and pick his brain for facts and then run back here and post them so I can at least *appear* knowledgable too....;D
[For now, really, I just sit on the back and grin. I'll have my own ride this spring]...LOL!